Polyimide polymeric blends

ABSTRACT

Polymeric blends of polyimide precursor resins and polyamides or polyesters, preferably in the form of liquid crystal polymers, provide polyimide products with excellent physical characteristics and injection molding capability.

BACKGROUND OF THE INVENTION

Aromatic polyimides have long been known, such as those described inEndrey, U.S. Pat. No. 3,179,631 and Gall, U.S. Pat. No. 3,249,588.Further improved polyimides were more recently discovered by Manwillerand Anton, and described in U.S. Pat. No. 4,755,555. Each of the abovepatents is hereby incorporated by reference.

Previous polyimides, with their resistance to high temperatures andoverall mechanical properties, have found wide acceptance as coatingsand fabricated parts used in technically demanding environments such asjet engines, business machines, automotive components and diverseindustrial equipment. However, despite the excellent performancecharacteristics of previously available polyimide compositions, theapplicability of these materials has been limited by tile intractibilityof many polyimides. Specifically, many aromatic polyimides cannot beformed appreciably in their final chemical configuration. Accordingly,the polyamic acid precursor previously was formed into the desired finalconfiguration, such as a film, prior to conversion into the polyimide.In the alternative, formed articles of polyimide have previously beenmachined into their desired shape.

While these techniques have proved to be satisfactory in tile past, itwould be desirable to provide a composition which combined theoutstanding high temperature performance of aromatic polyimides withinjection molding capability.

SUMMARY OF THE INVENTION

The present invention provides a polyimide composition which can beinjection molded and which exhibits thermal and physical characteristicscomparable to known polyimides.

Specifically, the present invention provides a blend of

(a) about from 99 to 20% by weight of at least one polymer which is meltprocessible at a temperature of less than about 400° C. and selectedfrom polyamide and polyester and, complementally,

(b) about from 1 to 80% by weight of polyimide precursor resin preparedfrom at least one aromatic diamine and at least one aromatic dianhydridein which less than about 98% of the polymeric units are converted topolyimide.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the discovery that certain blends ofpolyimide precursor resin and at least one polyamide or polyester,preferably in the form of liquid crystalline polymer (LCP), provide aunique combination of the properties characteristic of polyimidestogether with an injection molding capability.

A wide variety of polyimide precursor resins can be used in the presentinvention. Representative of polyimides which can be used are thoseprepared from aromatic diamines and dianhydrides as described in theaforementioned Endrey, U.S. Pat. No. 3,179,631 and Gall, U.S. Pat. No.3,249,588. Certain of those polyimides have been found to beparticularly satisfactory in the present invention, namely, those havinga rigid polymeric structure. Representative of such rigid polymericmaterials are those prepared using pyromellitic dianhydride (PMDA) andoxydianline (ODA); p-phenylene diamine (PPD) and PMDA; and3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA) and PPD. Thedianhydride and the aromatic diamine are generally reacted insubstantially equimolar quantities. However, excesses of dianhydride ordiamine can be used to beneficially modify the properties of the finalpolyimide. The reaction product of the dianhydride and the aromaticdiamine is a polyimide precursor resin, containing polyamic acid whichcan be thermally or chemically converted to polyimide according to knowntechniques.

In accordance with the present invention, the polyimide precursor resinis blended with at least one polymer which is melt processible attemperatures of less than about 400° C. Melt processible is used in itsconventional sense, that the polymer can be process in extrusionapparatus at the indicated temperatures without substantial degradationof the polymer. Such polymers include polyamide or polyester. Theblending is carried out prior to complete conversion of the polyamicacid moieties to polyimide. The blending should be done when less thanabout 98% of the polyamic acid units are converted to polyimide, andpreferably when less than about 85% of the polyamic acid units are soconverted. The percentage of unconverted polyamic acid units in apolyimide precursor resin can be determined using conventionalthermogravimetric analysis (TGA).

A wide variety of polyamides or polyesters can be blended with thepolyimide precursor resin. For example, polyamides which can be usedinclude nylon 6, nylon 6,6, nylon 610 and nylon 612. Polyesters whichcan be used include polybutylene terephthalate and polyethyleneterephthalate.

The fusible or melt processible polyamide or polyester can be, andpreferably is, in the form of a liquid crystal polymer (LCP). The LCPsare generally polyesters, including, but not limited to, polyesteramidesand polyesterimides. LCPs are described by Jackson et al., for example,in U.S. Pat. Nos. 4,169,933, 4,242,496 and 4,238,600, as well as in"Liquid Crystal Polymers: VI Liquid Crystalline Polyesters ofSubstituted Hydroquinones," Contemporary Topics in Polymer Science,1984, vol 5, pp. 177-208. Still other liquid crystal polymers aredescribed in Calundann, U.S. Pat. No. 4,219,461. The specific LCP usedin the present invention is not critical, so long as the basic amide orester moiety is present.

The polyimide precursor resin and the polyamide or polyester can beblended by any convenient technique, as will be recognized by thoseskilled in the art, including, for example, conventional mixers andextruders.

After blending, the conversion to the polyimide can be completed. Thiscan be brought about by conventional techniques, most typically thechemical or thermal conversion methods previously used in the art.

The physical properties of the resulting polyimide blend, after forminginto the desired final configuration, can often be further improved byheat treatment, using times and temperatures appropriate for the blendcomponents. In general, the heat treating involves exposing the moldedpolymer blend to an elevated temperature profile approaching but belowthe melting point of the polyamide or polyester, over a period of about2-24 hours. The heat treatment can be carried out in air, but preferablyunder nitrogen. Typical maximum temperatures are about 300° C. One heattreating procedure found to be particularly satisfactory for thoseblends based on LCPs is that described in Luise, U.S. Pat. No.4,247,514, hereby incorporated by reference. Heat treatment particularlyimproves the wear properties of blends based on LCPs over the LCPsthemselves.

The present polyimide blends often comprise fillers, to improve wear andfrictional characteristics, while retaining, to a large extent, theexcellent tensile properties of the polyimides. For example,carbonaceous fillers such as graphite, can be used. Other fillers whichcan be used with the present polyimide blends include molybdenumdisulfide, glass fibers, and tetrafluoroethylene polymers andcopolymers. The particular filler or fillers selected will, of course,depend on the effect desired in the final composition, as will beevident to those skilled in the art. It is often convenient toincorporate these fillers into the reaction mixture prior toprecipitation and blending with the polyamide or polyester, inquantities of from about 1% by weight of the polymeric blend to about80%, depending on the filler and the properties desired. Generally, lessthan about 50% filler is used. The form of the fillers will depend onthe function of the filler in the final products. For example, thefillers can be in particulate or fibrous form.

The polymeric blends of the present invention are useful in a widevariety of physical configurations, including, for example, moldedarticles, films and fibers.

The blends can be injection molded using conventional techniques. Thisinjection molding capability significantly broadens the applicability ofthe polyimides.

The present invention is further illustrated by the following specificExamples and Comparative Examples, in which parts and percentages are byweight unless otherwise indicated. However, the percent polyamic acid isbased on the percentage of polymeric repeat units in the form ofpolyamic acid as opposed to polyimide.

In these Examples:

Polyimide A is a polymer prepared by reaction of pyromelliticdianhyrdide and oxydianiline, according to the general procedures ofGall, U.S. Pat. No. 3,249,588, Example 3.

Polyimide B is the same polymer as A, with 15 weight % particulategraphite filler.

Polyimide C is the same polymer as A, with 40 weight % particulategraphite filler.

Polyimide D is a polymer prepared by reaction of pyromelliticdianhyrdide and oxydianiline, according to the general procedures ofManwiller et al., U.S. Pat. No. 4,755,555, Example 1.

Polyimide E is the same polymer as D, with 10 weight % particulategraphite filler.

Polyimide F is a polymer prepared by reaction of3,3'4,4'-biphenyltetracarboxylic dianhydride and para-phenylene diamine,according to the same general procedures, and containing 2.5 weight %graphite filler.

Polyimide G is a polymer prepared by reaction of3,3'4,4'-biphenyltetracarboxylic dianhydride and meta-phenylene diamine,according to the same general procedures, and containing 10 weight %graphite filler.

The polyimides or polyimide precursor resins were blended with varyingquantities of polyesters, as shown in the Tables. The blends weregenerally prepared using a 28mm twin screw extruder, except for Examples17 and 19. The extruder was operated with a barrel temperature of320-330° C., with the die at 330° C. The extruder was equipped with a ovacuum port, and a 3/16-inch (0.48 cm) die port. The screw was operatedat 150 rpm, to provide extrusion rates of 5-10 pounds (2.3-4.6 kg)) perhour. In Examples 17 and 19, the components were batch blended using aHaake mixer at 350° C. for 5-10 minutes.

The polyesters were in the form of LCPs. LCP-A is a copolymer of phenylhydroquinone, hydroquinone and terephthalic acid in a mole ratio of42.5:7.5:50. LCP-B is a copolymer of biphenol, hydroquinone,terephthalic acid, 2,6-naphthalene dicarboxylic acid and 4-hydroxybenzoic acid in mole ratios of 9.6:9.6:13.5:5.8:61.5.

Three 1/4"×1/4" pins are cut for each sample from the center edge of1/8" flex bars. The three pins are mounted on a 1.25" OD circular holderspaced 120 degrees apart, with their parallel axis (longitudinal axis offlex bar) oriented tangential to the 15/16" diameter mounting circle.The pins are loaded at 400 psi axially against a 1.25" OD×5/8" ID steelwasher of AISI 1018 carbon steel finished to 15 micro-inch (AA),rotating at 50 fpm velocity, as in a standard thrust bearing wear test.Wear factors obtained from measurements of the wear rate divided by theproduct of load (P) and velocity (V) at PV=20,000 are summarized belowfor blends and respective neat resins, in addition to measured staticand dynamic friction coefficients.

To convert reported property values to metric units, the indicatedvalues can be multiplied by the following factors:

    ______________________________________                                        English Unit Multiplication                                                   English Unit                                                                             Multiplication Factor                                                                           Metric Unit                                      ______________________________________                                        Kpsi       70.24             kg/cm2                                           ft-lb/in   5.44              kg-cm/cm                                         ______________________________________                                    

COMPARATIVE EXAMPLES A-I

To provide a basis for comparison, the mechanical properties and wearperformance of the substantially fully converted polyimides, polyesters,and blends of the polyimides and polyesters were tested. The results aresummarized in Tables 1 and 2 below.

                  TABLE 1                                                         ______________________________________                                        Mechanical Properties of LCP, and Blends with Polyimide Resin                      Blend                                                                    Ex-  Composition (wt %)                                                                          Tensile/            HDT                                    am-            Polyi-  Elong. Flex M                                                                              NIZod  (deg-                              ple  Polyester mide    (Kpsi/%)                                                                             (Kpsi)                                                                              (ft-lb/in)                                                                           C.)                                ______________________________________                                        A    LCP-A              9.9/0.35                                                                            1788  1.18   268                                B    LCP-A(60) A (40)  4.6/1.0                                                                               736  0.33   197                                C    LCP-A(70) C (30)   8.1/0.83                                                                            1074  0.39   236                                D    LCP-B             16.8/1.8                                                                             1015  1.92   239                                E    LCP-B(90) A (10)  18.7/2.0                                                                             1094  2.08   240                                F    LCP-B(60) A (40)  6.8/2.0                                                                               564  0.41   203                                ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Wear Performance of LCP and Polyimide Resin                                                 Kw      Friction of Coefficient                                 Example                                                                              Polymer      (x10-10)  Dynamic Static                                  ______________________________________                                        A      LCP-A        379,000   0.36    0.35                                    D      LCP-B        205,000   0.62    0.35*                                   E      LCP-B Blend  375,000   0.50    0.38                                    F      LCP-B Blend  148,000   0.48    0.49                                    G      Polyimide B**                                                                                 103    0.24                                            H      Polyimide G**                                                                                 16     0.11                                            I      Polyimide F**                                                                                 16     0.10                                            ______________________________________                                         *Severe noise and vibration.                                                  **Measured at PV = 25,058.                                                    (P = 187 psi  V = 134 fpm.)                                              

EXAMPLE 1-8

In Examples 1-8, blends were prepared from a polyimide precursor resinbased on polyimide (PI-F), with varying concentrations of unconvertedpolyamic acid (PAA). The polyimide precursor resin was blended withLCP-A and LCP-B, in the quantities indicated in Tables 3 and 4. LCP-Awas used in Comparative Example A and Examples 1-2. LCP-B was used inComparative Example B and Examples 3-8.

The mechanical properties of the blend of Example 4 and the polyester ofComparative Example D were tested with and without heat treatment. Theheat treatment was carried out at a maximum temperature of 305° C. for aperiod of about 28 hours under a nitrogen atmosphere. The heat treatmentwas carried out by heating the samples from room temperature to 200° C.over a period of 2 hours; heating to a temperature of 200-305° C. for7.5 hours; holding at 305° C. for 16 hours, and cooling to roomtemperature over a 2-hour period. The treatment was carried out undernitrogen, with the samples laid on a porous metal tray which was coveredwith fiberglass cloth.

The test results are summarized in Tables 3, 4, and 5.

                                      TABLE 3                                     __________________________________________________________________________    Mechanical Properties of LCP and Blends with Polyimide Precurser Resins       Blend Composition (wt %)                                                                        % of Repeat                                                                          Tensile/Elong.                                                                        Flex M                                                                            NIZod                                                                              HDT                                 Example                                                                            LCP    PI-F  Units  (Kpsi/%)                                                                              (Kpsi)                                                                            (ft-lb/in)                                                                         (deg-C.)                            __________________________________________________________________________    A    100                  9.9/0.35                                                                             1788                                                                              1.18 268                                 1    90     10    0.2    12.3/0.73                                                                             1591                                                                              0.53 247                                 2    70     30    0.2     7.1/0.66                                                                             1192                                                                              0.43 222                                 D    100                 16.8/1.8                                                                              1015                                                                              1.92 239                                 3    90     10    1.0    9.6/1.6 747 0.62 225                                 4    70     30    1.0    15.6/2.4                                                                              934 3.40 234                                 5    70     30    0.37   8.4/1.5 653 0.59 231                                 6    70     30    0.15   6.5/1.2 633 0.43 224                                 7    70     30    0.02   6.3/1.1 751 0.56 234                                 8    50     50    1.0    7.2/1.8 646 0.90 236                                 __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________    Mechanical Properties of LCP and Its Blend With Polyimide Precursor           Resin                                                                         After Heat Treatment                                                                            PAA                                                         Blend Composition (wt %)                                                                        (% of                                                                             Heat  Tensile/Elong.                                                                        Flex M                                                                            NIZod                                                                              HDT                              Example                                                                            LCP-B PI-F   units)                                                                            Treatment                                                                           (Kpsi/%)                                                                              (Kpsi)                                                                            (ft-lb/in)                                                                         (deg-C.)                         __________________________________________________________________________    D    100   --     --  no    16.8/1.8                                                                              1015                                                                              1.92 239                                                    yes   21.6/2.0                                                                              1020                                                                              7.80 315                              4     70   30     1.0 no    15.6/2.4                                                                               934                                                                              3.40 234                                                    yes   18.6/2.4                                                                               921                                                                              4.80 316                              __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________    Wear Performance                                                              Blend composition (wt %)                                                                        PAA    Kw   Coefficient of Friction                         Example                                                                            LCP   PI-F   (% of units)                                                                         (x10-10)                                                                           Dynamic                                                                             Static                                    __________________________________________________________________________    A    100                 379,000                                                                            0.36  0.35                                      A-HT 100                 95,000                                                                             0.57  0.48                                      1    90    10     0.2    15,400                                                                             0.29  0.27                                      D    100                 205,000                                                                            0.62  0.35                                      D-HT 100                 54,000                                                                             0.44  0.50                                      3    90    10     1.0    39,000                                                                             0.28  0.37                                      4    70    30     1.0    95,000                                                                             0.39  0.49                                      4-HT                       780                                                                              0.28  0.18                                      5    70    30     0.37    1,400                                                                             0.27  0.29                                      6    70    30     0.15     326                                                                              0.24  0.24                                      7    70    30     0.02     355                                                                              0.34  0.26                                      8    50    50     1.0      373                                                                              0.25  0.25                                      8-HT                       154                                                                              0.29  0.31                                      __________________________________________________________________________

EXAMPLES 9-19

In Examples 9-19, the general procedure of Examples 1-8 was repeated,using LCP-B and polyimide precursor resin based on polyimides D and E.The resulting blends were tested as before, and the results summarizedin Tables 6 and 7.

                                      TABLE 6                                     __________________________________________________________________________    Mechanical Properties                                                         Blend Composition (wt %)                                                                        PAA (% of                                                                              Tensile/Elong.                                                                        Flex M                                                                            NIZod (ft-                                                                          HDT                              Example                                                                            LCP-B PI resin                                                                             units)                                                                              HT (Kpsi/%)                                                                              (Kpsi)                                                                            lb/in)                                                                              (deg-C.)                         __________________________________________________________________________     9   90    D  10  1.0      17.2/2.1                                                                              882 2.10  233                               9                      X  18.6/2.1                                                                              874 2.60  291                              10   80    D  20  1.0      13.9/2.3                                                                              718 1.20  228                              10                      X  15.4/2.7                                                                              690 1.50  284                              11   70    D  30  1.0      11.1/2.1                                                                              609 0.80  221                              11                      X  12.2/2.8                                                                              573 1.10  282                              12   90    E  10  1.0      13.9/2.2                                                                              793 2.80  226                              13   80    E  20  1.0      12.7/2.2                                                                              744 1.33  224                              13                      X  13.9/2.2                                                                              755 2.75  291                              14   70    E  30  1.0       7.6/1.6                                                                              597 1.25  224                              14                      X   8.5/1.8                                                                              637 2.51  279                              15   70    E  30  0.79     11.1/2.7                                                                              634 1.63  230                              15                      X  10.3/2.4                                                                              620 2.48  316                              16   70    E  30  0.14      8.3/1.1                                                                              534 0.93  219                               17* 63.5  E  36.5                                                                              0.14      5.1/1.7                                                                              439 0.30  192                               17*                    X          404 0.48  238                              18   60    E  40  1.0       5.1/1.2                                                                              462 0.82  207                              18                      X   5.6/1.6                                                                              478 1.62  262                               19* 50    E  50  0.79      4.8/1.5                                                                              421 0.30  184                               19*                    X          402 0.45  234                              __________________________________________________________________________     *batched blended                                                         

                                      TABLE 7                                     __________________________________________________________________________    Wear Performance                                                              Blend composition (wt %)                                                                        PAA (% of                                                                           Kw    Coefficient of Friction                         Example                                                                            LCP-B PI resin                                                                             units)                                                                              (x10-10)                                                                            Dynamic                                                                             Static                                    __________________________________________________________________________    D    100                205,000                                                                             0.62  0.35                                      D-HT                    54,000                                                                              0.44  0.50                                       9   90    D  10  1.00  488,970                                                                             0.39  0.40                                      10   80    D  20  1.00  48,390                                                                              0.44  0.33                                      11   70    D  30  1.00  12,840                                                                              0.40  0.47                                      12   90    E  10  1.00  145,700                                                                             0.37  0.42                                      13   80    E  20  1.00  59,950                                                                              0.39  0.39                                      14   70    E  30  1.00   1,830                                                                              0.30  0.28                                      15   70    E  30  0.79  11,900                                                                              0.33  0.33                                      15-HT                     290 0.29  0.19                                      16   70    E  30  0.14   1,800                                                                              0.31  0.31                                      17   63.5  E  36.5                                                                              0.14  68,400                                                                              0.38  0.34                                      17-HT                    2,780                                                                              0.40  0.39                                      18   60    E  40  1.00   2,830                                                                              0.32  0.35                                      __________________________________________________________________________

I claim:
 1. A particulate polymeric blend of(a) about from 99 to 20% byweight of at least one polyamide which is melt processible at atemperature of less than about 400° C. and, complementally, (b) aboutfrom 1 to 80% by weight of polyimide precursor resin prepared from atleast one aromatic diamine and at least one aromatic dianhydride inwhich less than about 98% of the polymeric units are converted topolyimide.
 2. A polymeric blend of claim 1 wherein the polyamide is aliquid crystal polymer.
 3. A polymeric blend of claim 1 wherein lessthan about 85% of the polymeric units in the polyimide precursor resinare converted to polyimide.
 4. A polymeric blend of claim 3 wherein lessthan about 40% of the polymeric units in the polyimide presursor resinare converted to polyimide.
 5. A polymeric blend of claim 1 furthercomprising at least about 1%, by weight of the polymeric blend, offiller.
 6. A polymeric blend of claim 5 wherein the filler is inparticulate form.
 7. A polymeric blend of claim 6 wherein the fillerconsists essentially of graphite.
 8. A polymeric blend of claim 1wherein the polyimide precursor resin is the reaction product ofpyromellitic dianhydride and oxydianiline.
 9. A polymeric blend of claim1 which has been heat treated at an elevated temperature for a period ofabout 2-24 hours.
 10. A polymeric blend of claim 5 wherein the fillerconsists essentially of polytetrafluoroethylene.
 11. A polymeric blendof claim 5 which has been heat treated at an elevated temperature for aperiod of about 2-24 hours.